Re: [Paddlewise] Spare the gelcoat -- pros & cons of skin-coat boats

On Fri, Jun 06, 2003 at 03:00:23AM -0700, Dave Kruger wrote:

> 3. The quote from Derrer is somewhat out of context.  In one case,
> he uses a polycarbonate layer __in place of__ gel coat ("A
> Carbonlite 2000 skin replaces the gel coat in a composite kayak").
> See: http://eddyline.com/kayaks.cfm

I wasn't using the Derrer quote to suggest that he was a proponent of
using no over-layer on top of the fiberglass/kevlar laminate.  Just
that he too has argued that gelcoat doesn't do much to make a
"stronger" boat, which it seems is the popular perception.  I'm sorry
if that wasn't clear.  My mistake.

> Note that none of their "Legacy Composite" (= FRP) models are in
> normal production any more.

No, their not.  But I believe this is half a business-based decision
(it's more expensive to produce three variants of each model
[Carbonlite, Modulus, *and* Legacy Composite], than just the present
two), and half an "I'm going to prove my (Derrer's) point" basis.

> They would have needed a UV protector, as do their Modulus versions.
> Those Modulus boats must be heavier than FRP boats of equivalent
> rigidity (note: I did not say strength, because the Carbonlite 2000
> layer is strucural).

Actually, I believe they say their Modulus boats are lighter than
would be an equivalent model using gelcoat.  I don't know if that is,
or is not, the case in practice.  For it to be so, I guess one of two
things would need to be true.  One - the two approaches would use the
same thickness laminate, and the polycarbonate shell would provide a
weight savings over the use of gelcoat on the same design.  Or two -
the polycarbonate shell may weight the same as (or more than) the
gelcoat equivalent, but its structural make-up allows for the use of a
thinner laminate underneath.

FWIW, according to Eddyline, the polycarbonate sheets they start out
with for the Modulus boats are thinner than the ones they use for the
Carbonlite models.  But, I believe they can form them in the same
molds.

Now if you really want to get Mr. Derrer started, ask him about
British boats such as NDK and VCP.  He insists he can build kayaks
that are just as strong as the 60-65 lb. NDK and VCP expedition boats,
and bring the weight in at around 48 lbs.  Now, I'm not talking about
"strong enough to do the same job, but ultimately not as strong as the
NDK and VCP designs" (which would imply he thought the Brit-boats
overbuilt), but rather "just as strong as those other designs" (which
implies he thinks the Brit-boats to be badly built.  That is an
argument I've heard from more than one designer on this side of the
pond.  But that is yet another can of worms.

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